High-frequency apparatus



July 9 1946.

w. c. HAHN HIGH FREQUENCY APPARATUS Filed April 26, 1941 3 Sheets-Sheet 1 Inventor: William C. Hahn,

His Attorney. J

Jul 9,1946. w. c. HAHN 2,403,795

arm: FREQUENCY APPARATUS Filed April 26, 1941 3 Sheets-Sheet 2 Inventor: William C. Hahn,

b x am y Hi s zttofneg.

July 9,1946. w. c. HAHN 2,403,795

HIGH FREQUENCY APPARATUS Filed April 26, 1941 5 Sheets-Sheet 3 fig. /0.

Inventor; WiHiam C. Hahn,

y z mw Hisv Attovn eg.

Patented July .9, 1 946 HIGH-FREQUENCY APPARATUS William C. Hahn, Scotia, N. Y., assignor to Gen-. eral Electric Company, a corporation of New York 1 Application April 26, 1941, SerialNo. 390,527

11 Claims.

The present invention relates to ultra high frequency apparatus utilizing the principles of velocity modulation and is considered useful in connection with high frequency oscillators, amplifiers, detectors, etc.

It is a primary object of the invention to pro- 'vide ultra high frequency apparatus which is capable of realizing high power output and which is characterized by a high degree of stability and reliability in operation. In this connection an important feature of the invention consists in an arrangement in which a stream of charged particles (e. g. electrons) is caused to traverse an elongated chamber which is of continuously conductive character and which is subdivided into a number of intercommunicating and mutually coupled sections each of which is individually resonant at a common frequency. It is shown herein that by properly correlating the velocity of the charged particles tothe longitudinal dimensions of the various chamber sections, useful high frequency energy conversion effects may be obtained by the mutual reaction of the charged particles and the structural elements of the chamber. For example, in accordance with one mode of use of the invention, the charged particles may be made to maintain the chamber in a condition of continuous resonant excitation such that it may be used as a fixed frequency oscillator for the generation of high frequency waves,

Thefeatures of the invention desired to be protected herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with thedrawings, in which Fig. 1 is a longitudinal sectional view of a discharge apparatus suitably embodying the invention; Fig. 2is a cross section taken on line 2-2 of Fig. 1; Fig. 3 represents a single section of the discharge chamber of Fig. 1, modified in a manner which assists in explaining the operation of the invention; Fig. 4 is a diagrammatic view representing the circuit analogue of the structure of Fig. 3;v Fig, 5 is a fragmentary view also useful in explaining the invention; Fig. 6 is a longitudinal section of a modified embodiment of the invention;*-Fig. 7 is a cross section taken on line 1-1 of Fig. 6; Fig. 8 shows a further modification; Fig. 9 is a cross section taken on line 99 of Fig. 8; Fig. 10 illustrates astill further modification; Figs. 11 and 12 joint- 1y illustrate a still further modification; and Fig. l3shows the application of the invention to an amplifier. v

Before proceeding to a detailed description of the invention it will be helpful to consider briefly some of the principles of velocity modulation as the same are set forth, for example, in my prior Patent2,220,839, granted November 5, 194D.

In the aforesaid patent it is pointed out that if a uniform stream of charged particles is caused to traverse a region which is subjected to cyclically variable potential gradients, the various elemer ts of the stream will be differently afiected as to velocity. That is to say, if the particles are electrons',those electrons which traverse the given region when the gradient in it is positive will be accelerated, while electrons which enter the re gion during periods of negative gradient will be decelerated In the event that the potential applied to'tlie said region is of cyclically reversible character, :thepo'rtion of the electron stream issuing from the "region will be' characterizedby alternate components, of high and low velocity, this condition corresponding to so-called (velocity modulation ofthestream. V g

Briefconsideration will show that if a velocity modulated electron stream is permitted to continue alonga fixed path, a regrouping of the electrons will occur 3S a result of the tendency of the fasterelectrons to catch up with the slower ones. Consequently, after an appreciable interval of time,the stream will assume a charge density modulated character in the sense that it will possess anunequal space distribution of electrons.

' The present invention makes use of the phenomena describedabove in that it employs the expedient of successively producing velocity modulation. of anelectron stream and thereafter converting the velocity modulation into chargedensity modulation for the accomplishment of certain desired results.

, Referring particularly to Fig. 1, there is shown an exemplary embodiment of the invention in the form of an elongated evacuated discharge tube terminating at one end in a bulbous glass portion in. The part II) includes a reentrant stem H which terminates in a press [2 for supporting a V filamentary cathode I4 and a pair of aligned conductivelmetallic) cylinders l6 and H. The former of the two cylinders serves primarily to confine the electrons released from the cathode [4 to 'aiconcentratedbeam and to this end may be either connected directly to the cathode as shown or maintained a few volts negative or positive with respect to it. The cylinder ll acts to accelerate the electron stream and is accordingly biasled to'a'f suitable positivepotential, say several hundred volts, with respect to the cathode,

' In" addition to the bulbous part It), the tube envelope includes an elongated hollow conductive structurewhichis designated as a whole by the numeral 20 and which is joined to the part In by means of a hermetic seal indicated at 2| A conically shaped metallic member 22 covers the seal between the glass and metal parts of the ub and r es to hi ld i from the fl pt o t e high potentials which may be developed within the tube during its use.

The tube part is of continuously conductive character, being preferably constituted of an assembly of copper or brass rings, and is characterized internally by a series of recurrent discontinuities. In the particular embodiment shown in Fig, 1 these discontinuities comprise a number of perimetrically complete (e. g. annular) wall parts to 2! which efiectivel subdivide the main body of the tube into a series of identical sections. These wall parts define between them a succession of gaps 3D to 33 which are successivel traversed by the stream of charged particles projected from the cathode 14. After traversing the gaps, the stream is collected by'a metallic end wall 35 which closes the extremity of the tube.

In the operation of the tube, the structure 20 may be maintained at ground potential and the cathode at one to several thousand volts below ground. This may be accomplished by the use of a D. C. voltage source which is illustrated conventionally as a battery 36 and which also serves to bias th electrode I! to the desired potential. The electron stream developed by the coaction of the various tube elements may, if desired, be maintained in focused condition by the provision of a direct current excited magnetic focusing coil 31.

In order to understand the practical operation of a structure of the character outlined in the foregoing, it should be noted that the part 20 may be viewed in two aspects. In the first it comprises a series of electrode elements for influencing the electron stream traversing it. In the second it may be considered as a unitary resonant system adapted to be maintained in continuous oscillation by the reaction of the electron stream. The relative dimensions of the various parts of the structure should be such as to permit it to function satisfactorily in both of these capacities.

In order further to clarif the matters just referred to, it will first be assumed (subject to later justifi'cati'on) that the structure 2'0 may be maintained in a condition of sustained oscillation (resonance) such that cyclicall reversible potential gradients appear across the gaps 30 to '33 inclusive. It is assumed further that the circumstances of operation are such as to cause the gradients existing in the various gaps tobe of similar magnitude and to have a common direction at any given time. (It will be pointed out at a later point that this represents only one of several equally possible modes of operation.) Under these circumstances it is clear that the electron stream traversing the various gaps necessarily undergoes some degree of velocity modulation. Moreover, such modulation is most pronounced if the electron transit time between corresponding points in two adjacent gaps corresponds at least approximately to an integral number of complete cycles of potential variation at the operating frequency of the apparatus.

With the above specified conditions fulfilled, it is apparent that electrons which reach the first gap 39 in such time phase as to be accelerated by the potential gradients existing across the gap will be still further accelerated as they traverse the Various subsequent gaps. Conversely, elec trons which are decelerated at the first gap will be repeatedly decelerated at the remaining gaps. The net result will be that as the electron stream passes longitudinally through the structure 20 it will develop significant velocity differences from point to point and will, in itsmore advanced portions, become charge density modulated as the faster electrons overtake and become grouped with the slower electrons.

Under proper circumstances, the charge groups thus pr duced in the stream may be expected to release energy to the resonant structure in such fashion as to maintain it in continuous oscillation. In my prior Patent 2,222,902, it has been Shown in connection with a system which, from this standpoint, is analogous to that here being considered that the maintenance of sustained 0scillations requires that the average electron transit time between successive gaps shall depart somewhat from the value previously assumed herein, that is, from equivalence to an integral number of complete potential cycles at the operating frequency. The preferred amount of such departure is a function. of the number of gaps employed in the system as a whole, and is indicated in the following table, in which 0b represents the part of a cycle (one complete cycle being equal to 360 degrees) which is required for the transit of an electron from a given point in one gap to a corresponding point in the next succeeding gap.

Table Number of gaps 0b Degrees The significance of the foregoing table may be summarized by saying that most effective mutual reaction of the electron stream with the resonant structure 20 will occur when the longitudinal dimensions of th various structural parts are so correlated to the stream velocity and to the desired operating frequency as to bring about a value of 6s corresponding to the values indicated in the table. It should be noted in this connection that no change in operation will-occur if for any selected number of gaps the value of 9b given in the table is increased by 360 or by some integral multiple of that angle. Thus, if a six-gap system is to be used and design considerations make it desirable to employ an electrode length greater than that which would correspond to 335, equivalent results may be obtained by using 335 plus 360,or 695. It will be understood from a consideration of the table that in every case the average electron transit time from gap to gap will be on the order of the time consumed by an integral number of complete cycles of potential variation (at the desired operating frequency of the apparatus), but will depart therefrom by a fraction of a quarter-cycle of such variation.

The operation of the apparatus as so far described may be summarized by saying that the electron stream projected from the cathode I4 is modulated as it traverses the initial gaps in the resonant structure; that this modulation is effectively amplified by the occurrence of electron-grouping effects as the stream progresses longitudinally of the structure, and that a portion of the energy of the modulated stream is released to the resonant structure at the various gaps subsequent to the first gap to maintain the structure in continuous oscillation. On this latter point it is assumed that suflicient mutual- 2,4o3,79c. V V

space coupling exists between the varioussections of the resonant chamber to assure that the forced oscillation of the sections last traversed by the. electron stream shall be communicated to the sections first traversed by the stream so as terminally short circuited by the wall part 20a,-

\ and the two lines are joined by the axially exto maintainthese also in an oscillatory condition. It is found that such coupling exists to a satisfactory degree provided the various chamber sections are in communication withsone another through openings having a diameter which is not less than their. axial extent. This condition. is

obviously fulfilled in the arrangement illustrated in Fig. '1 in which the ratioof the diameterof the openings in the wall parts 25 to 21 tothe. length of such openings is on the orderof .2: 1. Assuming favorable circumstances ,(including an electron stream of adequate intensity), a sufficient, amount of energy may be released from s the apparatus as. a whole is obviouslyadapted for use as an oscillator for the generation and propagation of high frequency ignals. r

In order still further tov explain the matters referred-to in the foregoing, it will be helpful to examine briefly the factors. which control the resonant operation of a system suchv as that formed by the structure 20. This may be done most easily by reference to Fig. 3 which illus-- tratesby Way of example the third section of the structure and whichshows theextremities of this section as being closed by "conductive partitions 40 and 4| extending through the central planes of the wall parts 26 and 21. I

As thus modified, the section in question comprises a closed chamber including a cylindrical spaceB which is surrounded by and merges-(at the boundary X) into an annular space A. This chamber, lik any confined space bounded by'a conducting medium, is electrically resonant at various'frequencies determined'by the dimensionsand configuration of the space. r 1

- In order to analyze the properties of the chamber of Fig. 3 in a useful Way, one may set up Max wellsfield equations for 'theenclosed space and solve the equations in a manner consistent with the specified boundary conditions. In-an article published inthe Journal of Applied Physics for January 1941 at pages62 to 68 I have shown'one procedure by which such an analysis maybe carried out. This analysis includes the derivation or equations which permit the resonant frequen; cies' of a chamber of the type in question to be determined if its dimensions are known,'and which further allow a missing dimension to be calculated if the remaining dimensions andthe" desired operating frequency are taken as fixed.

The form of thesolution 'given'in the article mentioned above suggests that a structure of the type under consideration may be conveniently viewed ascomprising the combination or'two radial transmission lines (corresponding to the spaces A and B), the former comprising' the' op' posedannular surfaces of the parts 26and 21' and 'the latter being made-up or the 'disk-likepartitions llla'nd' 4|. The first lineis obviously of 'the "resonant chamber.

tendingsurfaces 26a and 21a. It may be assumed that from an approximate viewpoint, resonance will occur when, the impedance looking into the first mentioned transmission line (the line A) from its inner periphery is equal and opposite to the impedance of the second named transmissionv line as viewed from the region of its junctionv with the first line. In another manner of statement, this means that the effective inductance of transmissionv line A must resonate with the efieca tive capacitance of transmission line B; the, lumped circuit analogy of this situation being" represented in Fig. 4. In the latter figure, the various circuit elements are numbered to correspond insofar as possible to the equivalent structural elements of Fig. 3. The resulting combination includes inductive components 26' and. 21' which are balanced (at resonance) against a capacitive component B. a

Considerations of symmetry indicate that a large number of identical resonant chambers of. the character shown in Fig. 3 may be placed end-to-end and the partitions between them removed without modifying the conditions of'res onance of the various units. (This, of course, produces the construction of Fig. 1.) end section 30 there is some dissymmetry due to the necessity of providing in abutment with this section an open-ended tube 42 through which. the electron beam may enter the resonant chamber. (This .tube should have a diameter less than about .6 times the operating wave length and a length at leastseveral times its diameter in order to avoid radiation through it of highfrequency energy generated within the chamber 20.)

The effect of this dissymmetry may be compensated, however, by an end correction in the form of a reentrant annular collar 43 the function of which is to add effective inductance in the end chamber to correct for the reduced capacitance.

attributable to the presence of the tube 42.

During operation of a structure of the type under consideration, the flow of conduction current will obviously be confined whollyto'the walls most probable condition of operation, it will be pages 284 to 308 of the Bell System Technicalwholly unidirectional at any given instant,.flowing toward either one end orthe other end of the chamber. For either case a compensatory displacement current, flowing in the opposite direction, exists near the axial region of the chamber.

"From another point of view the structure of Fig. 1 may be regarded as a modified form of resonant wave guide, analogous to'the wave-guiding systems described by G. C. Southworth at Journal for April 1936. 'In the publication referred to it is pointed out that a continuous conductive tube filled with a dielectric medium may be used for the guided propagation of high frequency electromagnetic waves in spite of the apparent absence of a conductive return cir-, cult of the character usually regarded as necessary to any channelized fiow of electrical energy. The waves which may be propagated in this way include, among others, waves having electric force components which are-confined to the axial and radial directions and ;magnetic force components which are wholly azimuthal; such wavesbeing arbitrarily designated as -Eowaves. Under appropriate circumstances waves of definite frequency may be caused to For the Moreover, for theexist in a standing wavepattern within a wave guide of given dimensions,- this condition being taken to define resonance of the waveguide for the particular 1 frequency involved.

The. application to the present invention of the matters stated in the foregoing may Joe understood by reference to Fig. 5, in which the solid line structure 45 represents a tubular wave guide ofdimensions chosen to provide a particular resonant frequency for E waves.

Let it now. be assumed that the diameter of the' tube is diminished at periodically spaced regions. 46 to 43, for examplaby inward deformation of the tube wall. Due to the relationship .of the magnetic and electric force components in E0 waves, asdefined above, the volume afiected by the proposed change is that in which magnetic energy storage is predominant. Consequentl'y, the change reduces the inductance of the system without correspondingly varying its capacitance and thus tends .to raise the resonant frequency of the structure of a Whole. In order to onset this effect and to provide enough added inductance to restore the original condition of resonance, the diameter of the remaining p01- tions of the tube may be increased as indicated at 49', 56, and 52 so as to provide added volume for magnetic energy storage; With'this change the wave guide ought to function essentially as it did inits original condition in so far asresonant operation is concerned.

, It will be realized, however, that due to the existence ofv the gaps 54 to 56 a structure having the configuration indicated by the dotted line will be characterized, when in resonance, by the existence of periodically spaced and sharply defined variations in the axial potential gradient, which variations are not present in the smooth tube 45. In the use of the structure in a system in which an electron stream axially traverses the structure, these variations may be made to produce a significant reaction on the electron stream, and under .proper conditions to result in the occurrence of self-sustained oscillations. From'this viewpoint then, the dotted line structure of Fig. 5, although derived and described on the basis of waveguide principles, isthe functional equivalent of the chamber 20 of Fig. 1.,

- It .may also be noted at this point that any resonant system of the type under consideration.

is characterized by a theoretically infinite number of modes of resonance. It is, of course, in

tended that in practical use, a given apparatus shall be restricted to a single preselected mode of resonance by judicious choice of the operating conditions, including appropriate selection of the operating voltage and beamv current. On the other hand, some structures may well have a number of modes ofv operation, all of which-are realizable by the use of practically attainable operating conditions. It is, therefore, in no sense a departure from my invention to so modify the,

operating conditions of a given apparatus having a construction of the type disclosed herein asto procure its operation in a mode of resonance different from that specifically assumed in the foregoing. For example, a resonant structure such as, that shown in Fig, 1 and having an even number of gaps may be expected to resonate not only under such circumstances that the potential gradients inthe various gaps are at any-given time unidirectional (as above explained), but alsoin an alternative condition such that the gradients in alternate gaps are oppositely directed. fl h-is represents a useful condition of oper ation the scope-or thepresent-invention provided the electron transit time between successive' gaps is made to correspond approximately to an-oddnumbe'r (including unity) of'h'al'f-cycles of'potential variation so that cumulative acceleration anddeceleration effects are realized at the various gaps;

In the-designof a resonant system of the type under consideration (e. g. in Fig. 1) it is gener ally expedient'to assume ap'rac-ti'cal dimension for the interior diameter of parts 2-5, 26, etc; next, to select a convenient operating voltage; and from this and the desired frequency to compute the longitudinal dimensions of the system. This leaves still undetermine'd'the diameter of the chamber in the regions between the parts 25 to 21 but this may be calculated by the procedure given in the Journal of Applied Physics for January 1941 to which reference has already been made.

With the dimensions of thestructure thus determined, one may next compute the losses of the system (mainly resistance losses in the wall parts of the structure.) and decide upon a beam current sufficient to provide-for these losses and to permit useful-power to be taken from the system. Provided the chosen conditions of operation prove to bersuch as to assure the operation of the systemin its desired mode of resonance to the exclusion :of other and unwanted modes, the design may .be accepted as a practical one.

One advantage of electronic apparatus of the type herein described lies in the fact that all parts of theresonant structure are directly electrically connected and may therefore be maintained at a fixed D. C. potential. Thi means that the operation of the apparatus will be free from sporadic variations due to wall-charging or the like, irrespective of the number of cascaded' sections which are included.

An alternative type of oscillator, shown in Fig. 6, comprises a bulbous glass envelope portion which is joined at its open end to an elongated metal tube 6|. Areentrant stem 62 provided in connection with the glass part 60 supports the combination of a'cathode 63, a focusing electrode 64 and an accelerating electrode 65, these elements being adapted to project a stream of electrons axially of the envelope. Focusing and energizing means similar to those shown in Fig, -1 may be employed.

, Themetal tube I is closed at its extremity by :a transverse metal wall 66 which serves to collect the electrons after their traversal of the tube. The tube further surrounds and supports a series of, metallic partition-forming elements which subdivide the enclosed space in a manner analogous-to the parts 25 to 21 of Fig. 1. In this case, however, the partition-forming elements comprise a series of abutting rings 68 to H of relatively large diameter having smaller coaxial tubular elements 13 to 16 joined thereto by thin imperforate annular webs 18 to 8|. A passage for electron into the sectionalized chamber defined by the elements-just referred to is provided through" a tubular member 82 which connects with-thefirst-sectionof the chamber.

A system such as that shown in Fig. 6 may be made to-operate in much the same manner as the-apparatus of Fig. 1. That'isto say, assuming proper correlation of the electron velocity with the spacin of the rings and with the desired operating frequency, efiective mutual reaction of the-' electron stream-and the structure traversed by-itmay be expected to occur at the gaps be- 9 tween the rings 13-16 in .such a manner as to produce concurrent modulation of the former and excitation of the latter. The oscillations thus established in the space within the tube BI may be caused to produce useful external efi'ects'by means of a coupling loop 85 .which'connects with coaxial conductors 86 and 81 extending outwardly through the wall 66. J a f l It is found upon analysis that an annular space such as thatbounded'by thefl opposed webs I8 and I9 and the various conductive surfaces which are continuous therewith. presents a greaterfap+ parent inductance at its inner boundary than does a chamber such as the space A of Fi -3+ assuming like radial dimensions and spacing of partition centers. On the other hand, the'apparent capacitance. observed at the same boundarylooking toward the centralaxis of the chain-- ber,is identical. for the two structuresmsince theinductance of the outer space is variable with the lradialpdimensions of the partitioning elements,. this means that for a given diameter of central opening, theover-all diameter of the shown in Fig. 9-which serve to prevent undesired propagation of wave energy outwardly through the space during operation of the apparatus.)

versible potential gradients directed axially ofthe chamberrequired for resonance is less in the Fig.

6 construction than in that of Fig. 1. This permitsiapparatus embodying the former construction to be made in arelatively more'comp'act form M Calculation ,further shows that the internal losses of resonant structures of the type under consideration are. also mainly a function of the dimensions of the radially extendin parts. ,Consequently, in situations in whichit is important to keep such losses ata low/value, it advan-.

tageous'to employ the construction of Fig 6. The optimum design in this connection is believed to. be that in which the wa1l ;parts.13-f-8l..are made'as thin as is reasonably possiblesince this permits the radial dimensionsof these parts required for resonance to be made a minimum. In some instances the subdivision of the resonant chamber may advantageously be accomplished by other means than inwardly extending partitions such as are illustrated in Figs .'1 -'7. One such alternative embodiment is shown in Fig. 8, which illustrates only the resonant structure, the remaining components of the discharge tube being omitted in the interest of simplicity;

In this case the chamber within which oscillations are to be developed is in the form of an elongated conductive cylinder 90 which at one end is joined through a smaller cylinder 9! to a glass envelope, of which only a fragmentary portion 92 is illustrated. It is assumed that the envelope 92 contains means. (not showmffor projecting an annular streamrof electrons longitudinally of the chamber 90 as indicated by the arrows D.

(The electron source employed in this connection may comprise, for example, an arrangement of the type'described in application Serial No. 347,- 744 of Louis Tonks, filed July 26, 1940, Patent No. 2,276,806, dated March 17,1942 and assigned to th'esame assignee as the present application.)

Arranged coaxially within the chamber 90 there is provided an elongated conductive shaft 95 having mounted thereon a series of equally spaced conductive cylinders- 91l02, the cylinders being mounted on and electrically connected to the shaft by means of imperforate diaphragms as'indicated at I03. The cylinder 9-1 occupies a substantial portion of the'cross-section of the entrance tube SI and projects somewhat into the in terior of "the chamber 90. f (The annular space between the cylindrical parts 91 and 9| islcngitudinally subdivided by partitions IMF-best chamber may be expected to exist at the gaps which separate the various cylinders. Consequently, as the electron streamfpasses in proximity to these gaps, its constituent electronswill be variously accelerated and decelerated in such a manner as to produce'velocity modulation of the stream; If' the resonant structurewere excited from an external source, most eifective modulation' could be produced by making the electron transit timebetween corresponding points in adjacent gaps equalto an integral number of complete cycles of potential variation at the resonant frequency (or, for certain modes of operation, to an integral number of half cycles atsuch frequency). However, in order to assure the main tenance of sustained oscillations with the selfexcited arrangement shown, the spacing between adjacent gaps should be slightly less than that calculated to'give'theresult just specified. With this condition fulfilled, aportion of the oscilla; tory energy developed Within the chamber may be abstracted for external use by means of an appropriate coupling loopjl05. In this instance the'loop I05 connects with an antenna I06 which is wholly within thevacuum space, being terminally confined by a glass closure member 101.

Fig. lOiIIustratesa construction which combines certainof the features of Figs. 1 and 8, In this case, the resonant system comprisesan elongated cylindrical chamber H0 having an axially extendingconductive shaft I I I which bears afse- V 'ries of conductive cylindersjl I 3-H 6 inclusive. Each of the cylinders is surrounded by an annular conductive partition I20-I23 which still-further increases the degree of subdivisionof the cham ber. However, the annular passagesbetween the outer'surfaces of the member I] 5-416 and the inner surfaces of the members I20--'I'23 permit an electron stream to be projected longitudinally of the chamber. In the caseillustrated, the electron stream'comprises a single pencil of electrons E whichis injected into the chamber through'a tubular opening I28 and'which leaves the chamher at its opposite extremity through an aligned opening I29, being intercepted upon its issuance from the chamber by a collecting electrode I30. The electrode-3H0 is insulatingly supportedwith respect to the chamber from an insulating (e; g. glass) wall'l3l and isassumed to'be maintained at a potential adapted to assure the collectionof allth'e electrons.

Obviously the general considerations which have previously-been stated herein as governing 11 rounding structure at the gaps which it traverses near the end of its path. The oscillatory energy thus developed within the chamber may be utilized by the provision of a suitable output circuit (not shown).

The various structures which have been described in the foregoing have been illustrated as being of cylindrical character. It is to be understood, however, that this isnot an essential attribute of the invention and that other crosssectional forms may be adopted. For example, Figs. 11 and 12 represent, respectively, a crosssectional view and a partial longitudinal section of a chamber which, externally viewed, is of square configuration. It comprisesv a conductive enclosure I40 and a pluralityof transverse conductive partitions, of which those shown are numbered I 4| and I42. This construction, which in its complete form may be assumedt'to be generally similar to the tube shown in Fig. l (except for its cross-sectional configuration), may be expected' to operate in a manner generally analogous to that specified in-connection with the former construction, due allowance being made in the calculation of resonant frequency for the different boundary conditions imposed by the shape involved.

Still other and more, complex configurations, such as chamber of oblate cross-section, may also be employed.

Furthermore, while the. invention has soyfar been described solely in connection'with oscillations adapted for the generation: and transmission of high frequency waves, it is by no means limited to this use and may be alternatively "employed in' the amplification and detection of received signals. Fig. '13, for example,,schematical- 1y illustrates an amplifier embodying a resonant system of the general character of 'thatillustrated in Fig. 1.

The structure'referred to comprisesan elongated glass shaft portion I50 which encloses a cathode II, afocusing electrode I52 and a series of aligned cylindrical electrodes I53'-I55,inclusive. These latter electrodes are maintained atincreasingly positive potentials. by appropriate connection-to a battery 'I 51.

The central electrode I54. is subjected toahigh frequency signal which may be-derived, for example, from an. antenna I59 and which is applied to the electrodethrough an appropriate .circuit; illustrated diagrammatically as. comprising the. parallel combination of an inductance. I60 and a capacitance IBI. Asa resultof'the, potential variations of the electrode I54, the electron stream proceeding from the cathode. I5I will obviously become velocity' modulatedas .it traverses the-gaps between thiselectrode-and the electrodes I 53 and I 55. With appropriate dimensions of the electrode I54 the modulating effects may be made cumulative at the twov gaps.

After passage through the electrode I55, the modulated electron stream-is projected into a chamber I64 which is similar in structural form to the chamber of Fig. 1. However; the longitudinal dimensions of the various subdivisions of the chamber I64. are preferably'made such as to assure. that the electron transit time between corresponding points in adjacent sections corresponds as nearl as possible to-an integral-number of complete. cycles of potential variation, at the resonant frequency of the chamber. Under these circumstances, and for reasons previously given herein, there willbelittle. tendency for .the chamber to break into. self-sustained oscillations as a result of its mutual reaction with the electron stream-except in so far as the stream may be modulated prior to its. entranceinto the chamber. Such excitation of they chamber I64 as occurs. will be a result of the prior modulation of the electron stream by the electrode I54 and will be proportional to the amplitude of such modulation. However, the strength of the waves developed within the chamber I64 as a result. of its excitation by the modulated stream. may be very much eater than the strength of the received signal wave, thereby permitting amplification effects to be obtained. The amplifiedenergy developed within. the chamber, may be effectively utilizedby the provision of a couplingloop 1.66 Provided at an appropriate locationv within-the chamber'and having an external connection I61 adapted ,for coupling toa. suitable utilization de-. vice such asa detector (not shown).

Althoughthe invention. has been exemplified by reference to. devices operated with a pure electron discharge, it should be understood that. the principles set forth are applicablein their gen-. eral aspects to other. types of charged particles. For example, results generally similar to those described may be obtained by the useofla positive ion stream cooperating with. structures of the character referred to herein.

Moreover, while the invention has. been described in connectionwith particular structures and in particular modes of use, it will be under.-

stood that numerous modifications may bev made by those skilledin the art without actually. departing from the, invention. I, therefore, aim in the appended claims to cover all .such equiva lent variations as come within the. true spirit and scope of the ioregoing disclosure.

What I claim as new andldesire to secure by LettersPatentof the United States, is:

1. In combination, an elongated hollow conductive'structurea succession of discontinuities within the structure subdividing the enclosed space into. a series of spacer-resonant sections which are individually resonant. at a common frequency, all-the bounding surfacesof the varioussections being electricallyinterconnected by low resistance paths and there being a passageway extending longitudinally of the; structure for spatially interconnecting the-sections, andmeans for projecting. charges through the said. passageway to produce energy conversion effects by mutual reaction of, the said charges and the said resonant sections.

2., In combination, an elongated hollow conductive structure, a, succession ofv conductive elements, positioned at. regularly spaced intervals withinthe structure and. having extensions in a direction transverse to its, longitudinal axis. for subdividing it into a series of. space.-=resonant sections, all the bounding surfaces. of the various sections being electrically interconnected by low resistance paths and there being a passageway extending longitudinally of, ,thestructurefor spatially interconnecting the said sections, and means for projecting charges through the said passageway to produce energy conversion effects by mutual reaction of the said charges and the said resonant sections.

3. In. combination, a hollow continuously con-v ductive structure providing an elongated chamber, a plurality of conductive partitioning elements positioned at regularlyspaced, intervals along the length of the chamber and providing gaps between the. elements, the said elements subdividing thechamber into a plurality orsim- 13 ilar space-resonant sections each 'of which is individually resonant at thesame frequency, and means for projecting charged particles successively through the various sections and across the said gaps to produce energy conversion effects by virtue of the mutual reaction of the said resonant sections and the said particles.

4. In combination, an elongated hollow con-v ductive structure having inwardly projecting conductive wall parts at regularly spaced intervals along the length of its interior surface, said wall parts effectively dividing the space enclosed by the structure into a series of similar spaceresonant sections each of which is individually resonant at the same frequency, and means for projecting a stream of charged particles successively through the various sections to produce energy conversion effects by the mutual reaction of the said structure and the said stream.

5. A high frequency oscillator comprising means defining an elongated chamber of continuously conductive character, a succession of electrically connected conductive elements providing recurrent discontinuities within the chamber along its length, said elements effectively dividing the chamber into a plurality of space-resonant sections each of which is individually resonant at the same frequency, the various sections being connected by a passageway extendthe resultant wave energy for use external to the said chamber.

8. In combination, an elongated hollow conductive structure, a series of axially aligned tubular conductive elements positioned within the structure and extending longitudinally thereof, the said elements being mutually spaced to provide gaps between their adjacent extremities, conductive wall partsextending between the said elements and the lateral walls of the said structure for supporting the elements and for connecting them electrically to the structure, said wall parts dividing the structure into a series of similar resonant cavities which are connected through the axial openings in the said tubular elements, and means for projecting charged particles successively through the said tubular elements and across the said gaps so as to produce energy conversion effects by the mutual reaction of the particles and'the said resonant cavities.

9. High frequency apparatus including a hollow conductive structure defining an elongated chamber, a series of axially aligned electrically connected conductive bodies supported centrally within the said structure and extending longitudinally thereof, the said bodies being mutually produce energy conversion efiects resulting in the generation within the structure of high frequency electromagnetic waves.

10. High frequency apparatus including a hollow conductive structure defining an elongated chamber, a series of axially aligned cylindrical me the space enclosed by the structure into a v series of similar space-resonant sections each of which-is individually resonant at a common freelongatedchamber, a succession of conductive ele- V ments providing recurrent discontinuities within the chamber along its length, said elements effectively dividing the chamber intow'a plurality of space-resonant sections each of which is individually resonant at the same frequency, thevarious sections being connected'by a passageway extending longitudinally of the chamber, and there being an opening in the said chamber of such constricted dimensions as to inhibit the propagation through the opening of electromagnetic waves of the said frequency, means including a cathode outside the chamber for projecting electrons longitudinally ofthe chamber through the said opening and passageway, thereby to maintain the chamber as a whole in a state of resonant excitation by the generation within it of electromagnetic waves of the said frequency. and means for abstracting em a portion at conductive bodies supported centrally within the said structure and extending longitudinally thereof, the said bodies being mutually spaced to provide gaps between them and serving to divide the said chamber into a plurality of similar sections, each resonant at the same frequency, conductive means materially smaller in diameter than the said cylindrical bodies for directly connecting the various bodies along a line which is coincident with their common axis, and means to project charged particles longitudinally of the chamber in proximity to the said conductive bodies, thereby to maintain the chamber in a condition of resonant excitation by virtue of the mutual reaction, of the charged particles and the various conductive components of the apparatus.

11. High frequency apparatus comprising a hollow conductive structure defining an elongated chamber and having inwardly projecting conductive wall parts at regularly spaced intervals along the length of its interior surface, a series of electrically connected conductive bodies supof resonant excitation.

C. HAHN. 

